Quarter-wave reflecting plate with support core of resin-impregnated paper honeycomb



85AM ROOM 3 4 3 m 5 6 June 9, 1964 ULLER 3,137,000

P1.[J.l= QUARTER-WAVE REFLECTING PLATE WITH SUPPORT CORE OF RESIN-IMPREGNATED PAPER HONEYCOMB Filed Aug. 8, 1960 2 SheetsSheet 1 June 9, 1964 H. D. FULLER 3,137,000

QUARTERWAVE REFLECTING PLATE WITH SUPPORT CORE OF RESIN-IMPREGNATED PAPER HONEYCOMB Filed Aug. 8, 1960 2 Sheets-Sheet 2 Fig.2

INVENTQR Mwm'T -"1 United States Patent QUARTER-WAVE REFLECTING PLATE WITH SUP- PORT CORE 0F RESEN-IMPREGNATED PAPER HONEYCOMB Hubert David Fuller, Watford, England, assignor to The General Electric Company Limited, London, England Filed Aug. 8, 1960, Ser. No. 48,006 Claims priority, application Great Britain Aug. 10, 1959 2 Claims. (Cl. 343756) conductors act jointly to modify a parameter of the incident waves. For example the passive aerial may act to redirect the incident waves in the manner of a lens or reflector, or to effect a rotation of the plane of polarisation of the waves.

A passive aerial of the above kind is usually required to have as little weight as possible particularly if it is to be mounted for angular displacement, the moment of inertia of the passive aerial then being an important factor. Although in these circumstances it is desirable to reduce the weight of the passive aerial, it is also in general desirable to retain a certain minimum rigidity. These two desiderata tend to conflict with one another and also with the need to satisfy the necessary electrical requirements of the passive aerial.

It is an object of the present invention to provide a form of passive aerial of the above-mentioned kind which overcomes at least partially the above difliculty.

According to the present invention a passive aerial comprises a substantially rigid dielectric element which is of generally honeycomb structural form, and a plurality of electrical conductors which are carried in a mutually spaced relationship by, and at least in close proximity to, the dielectric element so as to modify a parameter (for example the direction of propagation or the plane of polarisation) of an electromagnetic wave that has a predetermined radio frequency and which is incident upon the dielectric element.

The dielectric element may comprise a honeycomb structure having front and back surfaces between which the individual cells of the structure extend, and two skins of dielectric material which are bonded to the honeycomb structure to cover the two surfaces respectively. The electrical conductors may be disposed upon these skins.

The passive aerial may be for example a quarter-wave reflecting plate, that is, a reflector which in reflecting an electromagnetic wave produces a phase dilference between two mutually perpendicular components of that wave which is substantially equal to one half wavelength. According to a feature of the present invention a quarterwave reflecting plate comprises a substantially rigid dielectric element which is of generally honeycomb structural form, a plurality of elongated electrical conductors that are carried by the dielectric element to lie in a substantially parallel spaced relationship with one another in a common plane, and a further electrical conductor that is carried by the dielectric element and has a substantially planar face which is substantially parallel to, and which is separated through the dielectric element from, said common plane, the arrangement being such that an electromagnetic wave that has a predetermined radio frequency and a plane of polarisation which intersects said common plane at forty-five degrees to the elongated conductors, passes between the elongated conductors and through the dielectric element to be reflected back from said planar face of the further conductor, the presence of the elongated conductors imposing a phase difference between two mutually perpendicular components of the incident wave which overall is substantially equal to one half of the wavelength of the incident wave so that the resulting wave transmitted from the quarterwave reflecting plate has a plane of polarisation which is substantially perpendicular to that of the incident wave.

A quarter-wave reflecting plate according to the present invention, together with a radar aerial system including that plate, will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a front elevation, partly broken away, of a part of the quarter-wave reflecting plate;

FIGURE 2 is a sectional elevation of part of the quarter-wave reflecting plate, this section being taken on the line IIII of FIGURE 1; and

FIGURE 3 is a view of the radar aerial system including the quarter-wave reflecting plate of FIGURES 1 and 2.

Referring to FIGURES 1 and 2, the reflecting plate includes two fibreglass skins 1 and 2 which cover the front and back surfaces respectively of a paper honeycomb structure 3. Copper wires 4 are disposed in a parallel spaced relationship over the whole of the front surface of the fibreglass skin 1. The wires 4 are bonded to the skin 1 with a synthetic resin, the spacings between the wires 4 being sufficient to allow electromagnetic waves which are to be reflected by the reflecting plate to pass between them and into the honeycomb structure 3.

The fibreglass skin 2 carries on its front surface a zinc layer 5 which completely covers the whole of that surface, this layer 5 providing a reflecting surface for electromagnetic waves incident thereon in operation through the honeycomb structure 3.

The paper of the honeycomb structure 3 is impregnated with a synthetic resin and the skins 1 and 2 are bonded to the edges of the paper over the respective front and back surfaces of that structure to provide a substantially rigid dielectric element carrying the wires 4 and the layer 5. In order to provide added rigidity to the element another paper honeycomb structure 6, similar to the structure 3, is bonded to the back surface of the fibreglass skin 2.

The back surface of the honeycomb structure 6 is covered by another fibreglass skin 7, and a supporting ring 8 for the reflecting plate is bonded between the two skins 2 and 7. The reflecting plate is mounted in operation with a section of waveguide (not shown in FIGURES 1 and 2) projecting through both the ring 8 and a central hole 9 in the paper honeycomb structure 3. The inner edge of the structure 3 bounding the hole 9 is protected by a fibreglass strip 10, and protection is afforded to the outer edges of the two paper structures 3 and 6 in a similar manner by a fibreglass strip 11.

A radar aerial system including the quarter-wave reflecting plate described above with reference to FIG- URES 1 and 2, will now be described with reference to FIGURE 3 in which the reflecting plate is given the general reference 12.

Referring to FIGURE 3, the aerial system includes, in addition to the reflecting plate 12, a horn 14 for radiating electromagnetic waves that are supplied thereto from a waveguide 15 which projects through the central hole in the plate 12. The electromagnetic waves radiated by the horn 14 are directed to be incident upon the front surface of the reflecting plate 12 by a paraboloidal reflector 16.

The reflector 16 (part of which is shown broken away for clarity) is formed by metallic foil strips 17 which are spaced apart parallel to one another in expanded ebonite. The strips 17 form a paraboloidal reflecting surface for the waves radiated from the horn 14. The spacing between the strips 17 is substantially less than half the wave length of the incident waves, and each strip 17 lies substantially parallel to the plane of the electric vector of the waves from the horn 14.

The reflector 12 is mounted by means of the supporting ring 8 (not shown in FIGURE 3) for angular displaceanent relative to the horn 14 about two mutually perpendicular axes 18 and 19, and is so mounted that the wires 4 lie at substantially forty-five degrees to the plane of the electric vector of the waves incident thereon from the paraboloidal reflector 16.

Any wave incident upon the reflecting plate 12 from the reflector 16 may be considered as having two equal components, a first having an electric vector parallel to the wires 4, and the second an electric vector perpendicular to the wires 4. Each of these components is propagated through the honeycomb structure 3 (FIG- URES 1 and 2) to be reflected from the zinc layer (FIGURES 1 and 2), but the spacing between the wire 4 is less than half the wavelength of the incident wave so that these wires impose an inductive loading upon the first component. On the other hand there is no such loading imposed upon the second component, this second component having an electric vector perpendicular to the wires 4. Both components are reflected back through the honeycomb structure 3 from the layer 5 to be repropagated from the front surface of the plate 12.

The magnitude of the inductive loading imposed upon the first component of the incident waves is dependent both upon the diameters of the wires 4 and their spacings, and is such that after passage of the first component of the incident wave through the structure 3 in both directions there is a phase difference of one half Wavelength between the first and second components. The plane of the electric vector of the resulting Wave reflected from the reflector 12 is in consequence substantially perpendicular to that of the incident wave. As a result, the reflected wave is substantially unaffected by the presence of the reflector 16, and the direction in which that wave is transmitted from the aerial system is determinedby the angular position of the reflecting plate 12 about the two. axes 18 and 19.

The general honeycomb form of the plate 12 results in a low moment of inertia combined with an adequate rigidity so that rapid acceleration of the plate 12 about the axes 18 and 19 is possible. The honeycomb struc-, ture 3 not only provides the dielectric for the plate 12, but in addition contributes to the overall rigidity of that plate. Furthermore the plate 12 has been found to have very good electrical performance and this is thought to be due at least in part to the fact that, with the paper honeycomb structure 3, the dielectric constant between the wires 4 and the layer 5 is not very different from that of air.

It will be appreciated that it is necessary for the thickness of the structure 3 to be uniform over the whole of the reflector 12, and that this thickness should be accurately related to the operational wavelength. The paper honeycomb form of the structure 3 assists in the attainment of both of these requirements since this structure is formed by strips of paper, and it is the widths of these strips which determines the thickness. The strips of paper may be cut to the required width with a high degree of accuracy.

In one reflecting plate constructed as described above with reference to FIGURES 1 and 2, for operation at frequencies in the region of 9,375 megacycles per second, the thicknesses of the fibreglass skins 1, 2 and 7 are respectively 0.009 inch, 0.006 inch, and 0.009 inch, and the paper honeycomb structure 3 has a thickness which is approximately 0.4 inch. The wires 4 are 35 S.W.G. and are spaced apart by just over 0.25 inch. Both of the honeycomb structures 3 and 6 is of the kind which is supplied under the registered trademark Dufaylite as Core Grade B by Dufaylite Developments Limited, England.

Where a plate 12 of smaller diameter or of lower rigidity is required, it is possible to dispense with the honeycomb structure 6 together with the skin 7. In this case the thickness of the fibreglass skin 2 should preferably be the same as that of the skin 1.

The zinc layer 5 may be sprayed on the front surface of the skin 2, however, it has been found that this does not always provide a satisfactory bond between the layer 5 and the skin 2. In order to overcome this latter disadvantage the layer 5 may be bonded to the skin 2 by a method including spraying the zinc on one surface of a sheet of cartridge paper. The sheet carrying the zinc layer is bonded with a synthetic resin to the skin 2 so that the zinc layer is face downwards on the skin 2,

: and the paper backing is then washed off with water.

I claim: 1. A quarter-wave reflecting plate comprising: a substantially rigid dielectric element that comprises a resinimpregnated paper honeycomb structure that has mutually parallel front and back planar faces between which cells of the honeycomb structure extend, and two dielectric skins that are bonded to said front and back faces respectively, to cover thesetwo faces; a plurality of elongated electrical conductors that are carried by the said skin that is bonded to said front face to lie in a substantially parallel spaced relationship with one another in a common plane; and a further electrical conductor that is carried by the said skin that is bonded to said back face, to have a substantially planar face that is substantially parallel to said common plane; the arrangement being such that an electromagnetic wave that has a predetermined radio frequency and a plane of polarization which intersects said common plane at fortyfive degrees to the elongated conductors, passes between the elongated conductors and through the dielectric element to be reflected back from said planar face of said further conductor, the presence of the elongated conductors imposing a phase difference between two mutually perpendicular components of the incident wave which overall is substantially equal to one half of the wavelength of the incident wave so that the resulting Wave transmittedfrom the quarter-wave reflecting plate has a plane of polarization which is substantially perpendicular to that of the incident wave.

. 2. A quarter-wave reflecting plate according to claim 1 wherein the elongated conductors are metal wires, and the further conductor is a metal layer.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Missiles and Rockets, June 1958, pages 89, 91 and 95. 

1. A QUARTER-WAVE REFLECTING PLATE COMPRISING: A SUBSTANTIALLY RIGID DIELECTRIC ELEMENT THAT COMPRISES A RESINIMPREGNATED PAPER HONEYCOMB STRUCTURE THAT HAS MUTUALLY PARALLEL FRONT AND BACK PLANAR FACES BETWEEN WHICH CELLS OF THE HONEYCOMB STRUCTURE EXTEND, AND TWO DIELECTRIC SKINS THAT ARE BONDED TO SAID FRONT AND BACK FACES RESPECTIVELY, TO COVER THESE TWO FACES; A PLURALITY OF ELONGATED ELECTRICAL CONDUCTORS THAT ARE CARRIED BY THE SAID SKIN THAT IS BONDED TO SAID FRONT FACE TO LIE IN A SUBSTANTIALLY PARALLEL SPACED RELATIONSHIP WITH ONE ANOTHER IN A COMMON PLANE; AND A FURTHER ELECTRICAL CONDUCTOR THAT IS CARRIED BY THE SAID SKIN THAT IS BONDED TO SAID BACK FACE, TO HAVE A SUBSTANTIALLY PLANAR FACE THAT IS SUBSTANTIALLY PARALLEL TO SAID COMMON PLANE; THE ARRANGEMENT BEING SUCH THAT AN ELECTROMAGNETIC WAVE THAT HAS A PREDETERMINED RADIO FREQUENCY AND A PLANE OF POLARIZATION WHICH INTERSECTS SAID COMMON PLANE AT FORTYFIVE DEGREES TO THE ELONGATED CONDUCTORS, PASSES BETWEEN THE ELONGATED CONDUCTORS AND THROUGH THE DIELECTRIC ELEMENT TO BE REFLECTED BACK FROM SAID PLANAR FACE OF SAID 